v2.0: Supports deserializing accounts lt hash in snapshots (backport of #2994)

runtime/src/serde_snapshot.rs

@@ -57,10 +57,12 @@ use {
         thread::Builder,
     },
     storage::SerializableStorage,
+    types::SerdeAccountsLtHash,
 };
 
 mod storage;
 mod tests;
+mod types;
 mod utils;
 
 pub(crate) use {
@@ -419,6 +421,10 @@ where
             .map(|(epoch, versioned_epoch_stakes)| (epoch, versioned_epoch_stakes.into())),
     );
 
+    // This field is only deserialized (and ignored) in this version.
+    let _accounts_lt_hash: Option<SerdeAccountsLtHash> =
+        ignore_eof_error(deserialize_from(&mut stream))?;
+
     Ok((bank_fields, accounts_db_fields))
 }
 

runtime/src/serde_snapshot/types.rs

@@ -0,0 +1,48 @@
+use {
+    serde::{de, Deserialize, Deserializer},
+    std::{fmt, marker::PhantomData},
+};
+
+/// Snapshot serde-safe AccountsLtHash
+#[cfg_attr(feature = "frozen-abi", derive(AbiExample))]
+#[derive(Debug)]
+pub struct SerdeAccountsLtHash(
+    // serde only has array support up to 32 elements; anything larger needs to be handled manually
+    // see https://github.com/serde-rs/serde/issues/1937 for more information
+    #[allow(dead_code)] pub [u16; 1024],
+);
+
+impl<'de> Deserialize<'de> for SerdeAccountsLtHash {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct ArrayVisitor {
+            element: PhantomData<u16>,
+        }
+        impl<'de> de::Visitor<'de> for ArrayVisitor {
+            type Value = [u16; 1024];
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str(concat!("a u16 array of length 1024"))
+            }
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: de::SeqAccess<'de>,
+            {
+                let mut arr = [0u16; 1024];
+                for (i, elem) in arr.iter_mut().enumerate() {
+                    *elem = seq
+                        .next_element()?
+                        .ok_or_else(|| de::Error::invalid_length(i, &self))?;
+                }
+                Ok(arr)
+            }
+        }
+
+        let visitor = ArrayVisitor {
+            element: PhantomData,
+        };
+        let array = deserializer.deserialize_tuple(1024, visitor)?;
+        Ok(Self(array))
+    }
+}